A well bore is often drilled into a subterranean formation for recovering hydrocarbons, storing hydrocarbons, or injecting other fluids, such as carbon dioxide or aqueous fluids, for storage or disposal, or for recovery of deposited minerals or geothermal energy.
Typically the well bore is lined with a steel casing through which fluid is conveyed under pressure. The steel casing is cemented in the well bore in order to provide zonal isolation so that the fluid is extracted from or delivered to selected zones or layers of the formation and prevented from leaking into other zones or layers of the formation and leaking into the surface environment. The cement also bonds to and supports the casing.
For a well drilled into a rock formation, the well bore is typically drilled into the rock, and then the casing is placed into the well bore in the rock. A cement slurry is then pumped down through the casing, and the cement slurry flows out the bottom of the casing and rises up into the annulus around the casing in the well bore. As the cement slurry is pumped, the pressure and flow rate are recorded in order to detect abnormalities. If abnormalities arise, the pumping is not stopped because the setting of the cement before completion of the pumping would create problems. Instead, the cementing job is evaluated by logging after the cement is set, and if the cement evaluation reveals problems, they are corrected by an expensive recementing job. The recementing job typically involves perforating the casing with shaped explosive charges, and then injecting cement slurry down the casing and through the perforations into the annulus around the casing in the well bore.